Apparatus and method for surface property measurement with in-process compensation for instrument frame distortion

Abstract

The present invention provides an apparatus and method for performing surface property measurements, such as workpiece hardness and other material property measurements, with in-process compensation for instrument frame distortion and the like. The apparatus includes a substantially rigid base; a stylus coupled to the substantially rigid base, the stylus configured and selectively positioned to interact with a surface of a specimen at points along a central axis of the stylus; a proximity detector sensor coupled to the substantially rigid base, the proximity detector sensor disposed at a predetermined distance from the surface of the specimen and operable for sensing the predetermined distance between the proximity detector sensor and the surface of the specimen; and a proximity detector actuator coupled to the substantially rigid base, the proximity detector actuator operable for maintaining the predetermined distance between the proximity detector sensor and the surface of the specimen as the substantially rigid base and the stylus are moved with respect to the surface of the specimen along the central axis of the stylus.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)[0001]The present non-provisional patent application claims the benefit of priority of U.S. Provisional Patent Application No. 60 / 834,846 (Stuart T. SMITH et al.), filed on Aug. 2, 2006, and entitled “Method and Apparatus for Measuring Surface Properties Without Instrument Frame Stiffness Dependency,” the contents of which are incorporated in-full by reference herein.FIELD OF THE INVENTION[0002]The present invention relates generally to the precision metrology field. More specifically, the present invention relates to an apparatus and method for performing surface property measurements, such as workpiece hardness and other material property measurements, with in-process compensation for instrument frame distortion and the like.BACKGROUND OF THE INVENTION[0003]In general, instruments for performing surface property measurements on specimens, typically referred to as “indentation” tests, are commonly used in many laboratories. Specifically, wor...

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Benefits of technology

[0009]The present invention provides an apparatus and method for performing surface property measurements that are determined via the relationships between the geometries of styli and the relative penetration geometries into a specimen under known loading conditions. These measurements typically depend heavily on the characterization of the stiffness and stability of the instrument frame and stage. The methodology of the present invention significantly reduces the dependency on instrument frame and stage characterization. This is achieved by measuring, via a reference sensor, the relative location of a stylus and the surface of a workpiece as forces are applied. Using such an instrument, property values such as rate-dependent hardness, elastic modulus, scratch resistance, and plastic-elastic behavior may be determined with known uncertainties. Known and constant relative proximity between the reference sensor and the surface of the specimen effectively removes from the measurement process the effects of deflections in the instrument frame and stage.

[0014]In order to increase the operability of the surface property measurement instrument, positioning systems on which the specimen is mounted are considered. These positioning systems are typically feedback-based, whereby an operator may control the location of the test site on the surface of the specimen. This allows for indentation-scratch measurements where the applied load, depth of penetration, and / or geometry of the scratch may be of interest.

Problems solved by technology

Coincidences between the structural components of the surface property measurement instrument (i.e. metrology loops) and the structural components through which forces are transmitted (i.e. force loops) are minimized, being present only in the stylus applying a force and a mount for the stylus and force sensor, which is inherently unavoidable for any surface property measurement instrument that measures distortions in the region of applied forces.

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